Subterranean heat energy has recently received increased attention as a source of environmentally friendly and renewable energy. Currently, subterranean heat energy is harnessed by boring wells into the earth's crust to access reservoirs of heated steam, high pressure water and/or brine. The heated water or brine is effectively mined like other buried natural resources and brought to the surface where the fluid is used to operate turbines or utilized in other processes.
A common approach to extracting the subterranean heat energy is to actively mine dry steam within the reservoir and feed the steam through a turbine on the surface. Alternatively, produced fluids can be vaporized in a flash tank to generate steam or passed through a heat exchanger to vaporize a secondary working fluid. An inherent drawback of these approaches is that the mined fluid taken from the reservoir must be naturally or artificially replenished to maintain flowrates and decrease land subsidence. Artificially replacing the mined fluid through reinjection is typically undesirable as a significant portion of the energy collected must be devoted to pumping replacement fluid back into the reservoir creating a large parasitic load. Other drawbacks in the mining and replenishment of the subterranean natural resources includes seismic risks, subsurface disturbance causing subterranean environmental pollution of water reservoirs, scaling in the wells, poor efficiencies, the need for replenishing the working fluid lost during normal operation, the need for sufficiently permeable aqueous reservoirs, and the like.
Due to the in situ fluid requirements, the current state of the art is only able to operate in areas where in situ reservoir fluid is present. Also, the current state of the art of subterranean heat energy extraction is limited by the temperatures in which it may operate and therefore is only capable of extracting heat from a small fraction of the overall available subterranean heat resource.
Various closed-loop apparatus approaches have been advanced, which typically comprise positioning a subterranean heat exchanger within the subterranean reservoir and pumping a working fluid through the heat exchanger. The heated working fluid is returned to the surface for use in turbines or other processes. However, the current closed-loop apparatus approaches have drawbacks relating to efficient collection of the subterranean heat energy, controlling the rate of energy production, and maximizing productivity over a period of time to sustain the heat resource, among others. Unlike other types of power generation such as gas fired power generation, adjusting the production rate of energy harnessed from subterranean heat utilizing the current state of the art can be exceedingly difficult as the production rate is largely dependent on the uncontrollable conditions within the subterranean zone.
As such, there is a need in the art for improved systems, apparatus, and methods for harnessing subterranean heat energy in an efficient manner that is cost-effective without excessively depleting the source of the subterranean heat energy and for reliable and efficient adjustment of harnessing the thermal energy according to a given consumption rate. There is also a need in the art for improved systems and methods that can utilize resources of varying temperatures within various subterranean resources having varying fluid quantities.